How big can an image file be?

I want to post an image with a link but it says the file is too big. What is the correct size?

For what, a sig?

I just want it for a post

Oh ok. Best idea is to upload it somewhere and link it here. I use http://postimage.org/ after you upload it, it gives you the code to post it here.

I posted it from puu.sh but now its huge! how to fix?

If you use the website I listed it resizes the file for you. Click the size you want (800x600 is plenty).

I use tinypic or photobucket, both give you the right size for a forum on default with a code to copy and paste